FIGS. 6a-6b show an example of a conventional vibratory gyroscope.
As shown in FIG. 6a, a vibrator 4 in such conventional vibratory gyroscope includes a vibrating element 1 having a rectangular shape in cross-section, and two piezoelectric elements 2 and 3 adhered on two adjacent sides. As shown in FIG. 6b, the piezoelectric elements 2 and 3 are connected to impedance elements Z.sub.1 and Z.sub.2 through terminals 5 and 6, respectively, while capacitance elements 7 and 8 are disposed in parallel with the piezoelectric elements 2 and 3 and are connected to impedance elements Z.sub.3 and Z.sub.4 through terminals 9 and 10, respectively. The impedance elements Z.sub.1, Z.sub.2, Z.sub.3, and Z.sub.4 are further connected to a drive means 30 (as shown in FIG. 2b) through a common connecting terminal 11.
In the illustrated vibratory gyroscope, when an A.C. current for exciting the gyroscope is applied to the piezoelectric elements 2 and 3, the vibrator 4 vibrates with bending in the upward and downward directions as shown by an arrow 12 in FIG. 6a. Under such vibration, a self-induced vibration loop is formed by feeding back a differential output, from differential circuit 32, from terminals 5 and 9 as well as a differential output, from differential circuit 33, from terminals 6 and 10 to the drive means 30 (as shown in FIG. 2b). This provides vibrator 4 with continuous bending vibration in the direction shown by the arrow 12.
Under such vibration, when the vibrator 4 is rotated about its axis in the direction shown by arrow 13 in FIG. 6a, the vibrator 4 vibrates with bending due to Coriolis force in the direction shown by arrow 14 which is perpendicular to the direction of the self-induced vibration. This results in generating different voltages in the piezoelectric elements 2 and 3. Consequently, angular velocity may be measured by detecting, by means of detector 31 as shown in FIG. 2b, the difference in the generated voltages.
However, in general, the vibrating element 1 of a vibratory gyroscope inherently has errors in size and variations in its composition, and each piezoelectric element is different in its capacitance value. For this reason, the resonant frequency on each side of the vibrating element 1 on which one of the piezoelectric elements 2 or 3 is adhered is different from that on a side perpendicular to the aforementioned side. Accordingly, this brings about a difference in phase of the output voltages of the piezoelectric elements which prevents the user of the vibratory gyroscope from accurate measurement of angular velocity.
As the Coriolis force generated by rotation of the vibrator 4 increases in proportion to the rotational speed, this also increases the amplitude of the vibration shown by arrow 14 in FIG. 6a. On the other hand, the resonant frequency of the vibrator 4 generally decreases in proportion to an increase in amplitude of vibration. Consequently, when the vibrator 4 is rotated, a phase difference occurs in the output voltages of the piezoelectric elements 2 and 3 in relation to the rotational speed. This means that the output voltages do not increase in proportion to the rotational speed, and therefore, it is difficult to improve the accuracy in measurement of angular velocity.
Additionally, strain may occur in each of piezoelectric elements 2 and 3 mainly due to changes in temperature during periods of non-operation of the gyroscope. This means that electric charges may arise in the terminals 5 and 6 during periods of non-operation, and therefore may cause problems in that the level of the output voltage may be unstable for a period immediately after the gyroscope is again operated.
The present invention is intended to solve the above-mentioned problems encountered in a conventional gyroscope. Accordingly, the object of the present invention is to provide a vibratory gyroscope in which detection accuracy is improved and phase differences between the generated voltages in each piezoelectric element are eliminated. A further object of the present invention is to provide a vibratory gyroscope capable of sufficiently discharging the electric charges arising when the gyroscope is not in operation.